Telephone-exchange system



CLEMENT. XCHANGE S YSTEM. APPLICATION FILED JULY 15. 1907.

TELEPHON E Patented Aug. 3-, 1920.

7 SHEETSSHEET I.

an-uento'a gt EM ESSQ w; in doses E. E. CLEMENT.

TELEPHONE EXCHANGE SYSTEM. APPLICATION FILED JULY 15.1907.

1 348, 209. Pat d Aug. 3, 1920.

7 $HEETSSHEET 2.

I f f 1:? 5 1; if

Snwntpi E. E. CLEMENT.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED JULY 15,1907.

Patented Aug. 3, 1920.

7 SHEETS-SHEET 3.

avwento'c nun-mu" QX i tn eases E. E. CLEMENT.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED JULY 15,1907.

1,3 18,2( )9, Patented Aug. 3, 1920.

7 SHEETS-SHEET 4.

1/; TO I Snuento-n Wit eases E. E. CLEMENT.

TELEPHONE EXCHANGE SYSTEM.

1,348,209. APPLICATION FILED JULY I5, 1907- Aug 3 1 SHEETSSHEET 5.

E. E. CLEMENT.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED JULY 15,1907.

'1 348,209. Patented Aug. 3, 1920.

7 SHEETS-SHEET 6.

E. E. CLEMENT.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED JULY 15,1907.

Patented Aug. 3, 1920.

7 SHEETSSHEET 7- Suucntoz UNITED STATES PATENT OFFICE.

EDWARD E. CLEMENT. OF WASHINGTON. DISTRICT OF COLUMBIA. ASS-IGNOR, BY MESNE ASSIGNMENTS. TO JAMES R. GARFIELD, TRUSTEE, OF CLEVELAND,

OHIO.

Application filed July 15,

To (177 whom 2'? may conccrn:

Be it known that I, Enwann E. CLEMENT, a citizen of the United States, residingat \Vashington. District of Columbia, have 111- vented certain new and useful Improvements in Telephone-Exchange Systems, of which the following is a specification, reference being had therein to the accompany: in drawing.

Ely invention relates to telephone ex:- change systems. and particularly to sem automatic systems in which automatic switches or their equivalent are employed to effect interconnection of lines as determined by manual apparatus controlled through the agency of operators. My invention has for its object the provision of a number of sets of switching apparatus sufficient for the probable needs of the service, but not necessarily equal to the number of lines, and most desirably less than the number of lines; the provision of operators controlling sets less in number than the number of lines, and the distribution of the load. that is to say, the incoming calls, among the sets of switch ing apparatus, and among the operators. whereby uniform efiiciency in service may be attained.

For the sake of simplicity in description I shall specify herein automatic switches of the type known as Strowger selectors and connectors, the construction of such switches being well shown in Letters Patent No. 815.176 and No. 815,321, granted to Keith and Erickson. March 13. 1906. The circuits commonly employed with these switches are well known to those skilled in the art. I shall also specify a type of common battery line circuits and central office talking circuits which are considered standard, and generally known as two-wire bridged battery circuits. It is to be understood however that in specifying the apparatus and circuits mentioned they are used as types for purposes of description, and not as limiting the invention.

Stated in terms of the embodiment thus presented, the present invention comprises a number of groups of selector and connector switches less than the number of lines to be served; a number of primary selector switches normally set back to a fixed or zero position. and adapted to connect the calling lines with the said groups of selector and connector switches; a number of operators Specification of Letters Patent.

TELEPHONE-EXCHANGE SYSTEM.

1907. Serial No. 383,874.

selective keys and impulse transmitting means controlled thereby, with automatic secondary selector switches normally set back at a zero or idle position, and acting to connect the trunks from the primary selector switches to the operators apparatus when the calls are received, whereby the operators may talk with the calling subscribers, and may actuate the appropriate selector and connector switches to connect the calling and the -'anted lines.

By having all the primary and secondary selector switches normally set back to Zero, I effect a uniform distribution commencing always with the first trunk or the first posi tion. hen a subscriber calls in, current in his line energizes a relay which starts up a primary selector switch, said switch continuing to progress step by step until its wipers connect the terminals of an idle trunk. at which time the cut off relay of the line receives current from the switch circuit, the switch stops. and the secondary selector switch is started to connect the trunk to an idle operators circuit. An appropriate signaling means such as a lamp, is provided for each operators circuit, and the operator being thus apprised of a call is able to connect her telephone through her circuit to the trunk and thence to the calling line, and afterward to transmit impulses to the trunk and forward to its automatic first selector switch to secure connection with the line wanted. Testing and ringing of the wanted line are automatic.

The specific distinguishing feature of the invention claimed in the present case is that each trunk has a terminal selector switch by which a subscribers line may be connected in calling to an idle trunk line leading to a first selector switch; and each trunk line is provided with a switch starting up from'a zero or normally inoperative position to select and connect with the controlling and talking circuit of an idle operator. The ope 'ators circuit remains connected to the trunk as long as may be necessary to send the proper impulses for setting the switches which complete the connection. after which the trunk selector switch governing the operators circuits is returned to zero and remains disabled so long as the trunk is continuously in use. lVhen the subscribers have finished conversing. however, and have cleared out the connection,

Patented Aug. 3, 1920.

i rotary selector switch;

the right of the latter, and showing a selector and connector switch with their circuits throu h which the calling line may be connecte -With any one of a considerable number of other lines;

Fig. 4 is a diagram of circuits complementar to Fig. 2, intended to be placed at the rig t of the latter;

Fig. 5 is an end view of an improved Fig. 6 1s a section on the line of Fig. 5, Fig. 7 shows a modified form of switch similar to that shown in Figs. 5 and 6 some of the parts being omitted. Fig. 8 is a diagram showing the connections whereby the subscribers lines are connected with the trunk selector operating means in such manner that more than one switch cannot be operated by a single call.

Referring to Fig. 1, A is a subscribers station connected to the central ofiice by line wires 1 and 2 which are normally connected through the contacts of a cut off relay N to the line relay M and the ground, respectively, the line relay being connected to the main battery B through the wire 3. Line extensions 4 and 5 extend from the cut off relay to multiple bank contacts of switches S. Each switch S is a step by step selector switch and is what is called a single motion or rotary switch, having a spindle s journaled so that it can turn upon the axis and provided with a ratchet wheel by which it may be turned. This ratchet wheel is engaged by a stop or detent pawl controlled by the electromagnet s, and a stepping or working pawl controlled by the electromagnet 8 The mechanical construction of this switch is shown in Figs. 5 and 6 which will be hereinafter particularly referred to. The circuit of the electroma net s is controlled by the line relay M through this armature m for which purpose the front contact 7 of the relay is connected by wire 8 with the magnet 8 while the armature m is connected through the interrupter I with a battery wire 3. This interrupter is continuously operating and may consist, as shown, of a rotative cylinder having alternating insulating and conducting portions, one conductor being connected with the conducting portion and another with a pen ratchet on the spindle, and retrograde motion of the spindle being prevented b a stop pawl controlled by the magnet 8. he

spindle is provided with a return spring,

preferably a coiled spring, which has a constant tendency to turn the spindle back against the pawl of the magnet s, and when this pawl is released by the energization of the magnet will actually turn back the spin dle into its normal, zero, or inoperative position. The circuit of the ma net 8 in addition to being controlled by t e line relay M,

is also controlled by the relay R of the trunk. The release magnet s is controlled by the relays R and R.

In addition to the bank contacts 9 and 10 to which extensions 4 and 5 of the subscribers line are connected, each switch S is provided with multiple test contacts 11. The wipers 12 and 13 of the switch are adapted to engage, respectively with the bank contacts 9 and 10, while a test wiper 14 is adapted to engage with the bank contacts 11. From the wipers 12 and 13 are trunk extensions 15"and 16, the connection of which with the trunk lines 17- and 18 is controlled by a" trunk cut oil relay N, which is controlled by the relay R.

' The relays R and R are bridged between the two trunk conductors with the main batteryB between them. The tip relay R is connected at one side with the conductor 17, the other side being grounded, while the sleeve relay R is at one side connected to the free side of the battery B and at the other side to the trunk conductor 18. The tip relay R controls the clearings out of the automatic apparatus; the sleeve relay becomes energized when the switch S, of an idle trunk, picks up the calling subscriber and then closes the circuits of the magnets R and R which are respectively the stepping magnet of the secondary or operator selector switch S and a locking relay serving also as a cut oil' relay for shifting the control as the operators circuit is connected. The relay R is a cut off relay for the operators circuit wires 19 and 20. The functions of these several relays will best appear from the statement of their operation hereafter.

battery B, so as to send an impulse of current through the trunk wire 23. When the relay R is energized over the operators wire 20 it pulls up its armature to break apart the trunk wires 22 and 24 and connects the latter to the wire 26 which is connected to the free terminal of the battery B, thus sending an impulse of current forward over the trunk wire 24. W hen both of the relays R and R are simultaneously energized, they connect the operators wires 20 and 19 to the trunk wires 21 and 22, re-

spectively, so that the operator may connect her telephone to the wires 21 and 22 and communicate with the calling subscriber. It will be observed that the wires 21 and 22 are extensions of the trunk conductors l7 and 18 respectively, to which they are connected by means of condensers C, the condensers being provided to prevent confusion of battery current between the answering and calling ends of the trunk sections. It will also be seen that the conductors 23 and24 are respectively extensions of the trunk conductors 21 and 22. I

The test wiper 14 is connected by a wire 27 with a contact 28 through which circuit is broken when the relay R is energized and, therefore, when the trunk is in use. lVhen the trunk is not in use, and its switch S has been stepped into position to connect it with a calling line connection may be traced from the wiper through conductor 27, contacts 28 and 29, conductor 30 and cut-ofli relay N to ground.

It will have been observed that there is one switch S for each trunk, and in order that the switch of an idle trunk may be set in operation to connect a calling subscriber with that trunk, suitable apparatus is provided and further the apparatus is so constructed and arranged that it is impossible for a single call to set in operation more than one trunk switch at a time. The arrangement of the apparatus by which these results are accomplished, is shown in Fig. 8 from which figure portions of the apparatus which are not necessary to an explanation of the'features under consideration, have been omitted. Referring particularly to Fig. 8 it will be seen that the conductors 8, 8' and 8 which lead respectively to the stepping magnets .9 15 2s ,etc., the respective selector switches S, 19, 23. etc., are connected together by a conductor 31 so that the energization of any line switch M, 1M, or 2M at any subscribers station will operate to connect one side of the battery B through the interrupter I with all of the stepping magnets 8 18 etc. It

will be noted however, that the ground connection of these stepping magnets is made through the back contacts of the armatures 'r, 12", 21", etc., of the sleeve relays R, lli 2R, etc. It will be observed however, that although the ground connection of each of these stepping magnets is made through the back contact of its particular armature r, 11" or 21" the circuit thus partially made must be completed through the forward contacts of all of those armatures at one side of the armature in question. These forward contacts are only connected when their controlling relays are energized and'therefore,

only when the trunks to which they correspond are in use. It will now be apparent that it will be impossible for two trunk selector switches to be set in operation by the same call and also that the trunks will be progressively selected by succeeding calls. To illustrate, assuming that none of the trunks are in use, the armature 1" is the only one connected with ground as shown in the figure. If now a call is initiated by a sub scriber, intermittent battery connections will be made with all of the stepping magnets 8 18 etc. The magnet 8 however, being the only one having a ground connection, this magnet will be the only one energized and will step its switch S into connection with the calling subscribers line, the other switches ls, 28 etc., remaining unaffected. The trunk corresponding to the switch S having been thus placed in use, sleeve relay R will be energized and the ground connection through the armature r willbe placed upon its front contact so that armature is connected with the next armature 11" of a succeeding trunk. Ground is thus placed upon one side of the stepping magnet 18 so that upon a succeeding call from a subscriber the stepping magnet 18 will be energized, as was the magnet 8 and the switch 18 will be stepped into position to connect the second calling subscriber with the trunk corresponding to the switch 18. This second trunk having beenplaced in use, the armature 11" of this trunk will make a ground connection through its front contact for the armature 21" and stepping magnet 28 of the succeeding trunk and this operation of causing each trunk as it is brought into use to establish connections for the bringing of a succeeding trunk into operation upon the initiation of another call, is carried out to the limit of the apparatus. With the apparatus thus far described it will be seen that if a stepping magnet as 28 is receiving impulses through armatures as 17" and r of other trunks, and is stepping its switch 23 to connect its trunk with the calling subscriber, and either or both of the trunks through which the circuit of the magnet 28 is made, is or are cleared out, one or both of the armatures r and 11" will fall back and the circuit of the magnet 28 will be broken and the operation of the magnet will cease, leaving the switch 2S in whatever position it happened to be and confusion of the apparatus might result. To avoid this, contacts a and b are provided for each trunk selector switch except the one having its stepping'magnet connected with ground through an armature of its own trunk. The mechanical arrangement of these contacts is shown in Figs. 5 and 6 which will be referred to hereafter; these contacts are normally closed but are separated when the switch is in zero position. One of the con tacts is connected with the stepping magnet of its switch while the other is connected to ground. The ground connection of the stepping magnet is broken at these contacts,--when the switch is in zero position but after the swich has once left that position, the ground connection of the stepping magnet is maintained through these contacts until connection is established with the calling subscribers line regardless of whether trunks, through which the initial connection for the stepping magnet was made, are cleared out or not.

The trunk wires 23 and 24 extend as shown in Fig. 3 to the side-switch arms 8 and s of the selector switch S. This switch is of the Strowger type referred to in the beginning of my specification, having a main spindle arranged for both vertical and rotary movements, this spindle being placed at the axis of a set of contacts arranged in ten rows of ten each. Carried on the spindle are talking-circuit wipers s vhich cooperate with the bank contacts 8 and a test wiper 8 9 which cooperates with the multiple test contacts 8 The switch spindle is stepped up to bring its wipers opposite the desired row of contacts by means of the socalled vertical magnet 0 controlled through a relay V; and the rotary movement of the switch is brought about by means of a vibrator magnet 11' which makes and breaks its own circuit as it vibrates and is controlled by the relay T when the side switch arm 8 is in its second or intermediate position. It is unnecessary to give here any extended description of the circuits and apparatus of Fig. 3, all of these being old and well known to those skilled in the art. Q is a release relay of the switch and q is the release magnet governed thereby. The other parts of the apparatus as well as the circuit connctions will sufiiciently appear from the statement of operation hereinafter.

S designates a connector-switch which is designed to cooperate with a selector switch S It has a similar spindle carrying wipers s. The test is made on the tip or upper side of the line. The switch also contains line contacts in its banks arranged in rows of ten each. The spindle is stepped up to bring the wipers s opposite the desired row by means of a so-called vertical magnet v and is rotated step by step by means of a so-called rotary magnet 0 which in this case is not a vibrator but responds to distinctive current impulses, since the desired line is identified with a single pair of contacts only, and therefore the row of contacts a must be selected and the pair of contacts in the row afterward picked out by the wipers, before testing. In this resides the principal difference between the connector and selector switch, the purpose of the selector switch being to pick out and connect with an idle trunk line in any desired group. In the operation of the selector switch, therefore, the spindle is stepped up by means of definite and distinctive impulses to the row of contacts 8 and 8 representing the desired group (which may be either thousands or hundreds and in this case is hundreds), and after that, when the side switch has taken one step, the rotary magnet v takes control of'the switch and steps the spindle around continuously as long as the wiper s finds ground on the contacts 8 When this ground fails (the busy con tacts being grounded and the idle ones open) it means that an idle contact has been reached, and thereupon the side switch is moved a third step to cut off the rotary magnet and stop the wipers upon this ungrounded or idle contact.

The connector circuit contains a pair of condensers C for the reason that the forward impulses which work the switch must not be confused by the battery current supplied to the called subscriber. We may assume that the switches of Fig. 3 are both in v the same building with the apparatus of Figs. 1 and 2 although this is not at all necessary, and in such case the battery B shown separate in the two figures is of course the same battery. For the purpose of supplying talking current to the called subscriber, I connect this battery to the sleeve conductor 44 of the connector switch, through a relay R, and I ground the tip conductor 43 through the relay R which is the same as connecting it back to the battery. Thus, the main batter is also bridged across the conductors 43 an 44 through the relays R and R which as in the case of the relays R and R in Fig. 1 are wound to approximately 100 ohms each, but present high impedance to voice currents. R is a ringing relay, which controls the application of the ringing generator G to the called line and is itself controlled on the one hand by the relay R and on the other by the commutator K, which may be common to all the ringing relays of the exchange. The circuit of the ringing relay is indicated at 45, 46, 47, 48, 49 and 50, being terminated at the ground through the commutator on one end and at the battery wire 3 on the other end. This circuit is controlled by the relay R and this relay does not become energized until the side switch arms 8, s, s and 8 have made their last step so that the conductors 43 and 44 are completed from the condensers C to the wipers .9. Before this laststep of the side-switch is taken, the wipers s have been placed upon the terminals of the wanted line. andthe release relay Q has been applied to the tip side of the line for the purpose of testing. The circuit of this relay is as follows: 51, 52, 53, 541, 55, a, 56 to the tip wiper 8 If the line wanted is busy, there is a ground on the tip side, either by way of a relay R or by way of a relay R", depending on whether the line originated the call upon which it is enga ed, or was called by some other party. In cit er case the test or release relay Q will receive current; but if there is no ground because the line wanted is idle, then the test relay remains unaffected, the talking circuit is completed, and the sleeve wiper relay R becomes energized by current passing to the sleeve 8 and thence through the multiple contact 10 of the called subscriber (see Fig. l) and the cut-off relay N to ground. The

cut-off relay thereupon pulls up and the ringing relay'circuit is at the same time completed so that the commutator K takes control thereof. It will be observed that this circuit 4:647, etc., passes through a back contact on the relay R, which is controlled on one side by a pair of contacts under the foot of the spindle of the switch S and on the other side by front contacts of the tip relay R which does not pull up until the called subscriber answers. When this occurs, the relay R becomes energized, locks itself by way of Wires 50 and 57, and opens the ringing relay circuit 46, 47, 48, etc. The relay R is controlled by the subscriber in the intervals of ringing, for it will be observed that the commutator K has segments whereby it closes the ringing circuit at intervals only. IVhile this circuit is open, therefore, and the relay R deenergized in consequence, the subscriber has control of the relay B In order that the relay R may remain energized through the ringing intervals, I provide a special battery connection, as shown.

The arrangement of switches shown in Fig. 3 is sufficient for exchanges up to 1000 line capacity; but in order to provide for more than 1000 lines, another set of selector switches is required, interposed between the trunk ends of Fig. 1 and the switch S of Fig. 3. The capacity of the exchange can be increased indefinitely without altering these circuits by adding these sets or groups of switches in the well understood manner. The selector switches all have the same circuit as that shown at S and therefore I which is commonly called the vertical wire,

and to send the controlling impulses over the trunk wire' 24 which is commonly called the rotary wire. These so called rotary impulses serve to work the side-switch magnets T and T, and thereby to shift the side switches so as to bring into play successively the vertical and rotary magnets, the test relay, etc.

Referring now to the lower part of Fig. 1 and Fig. 2, I have therein shown an operators equipment and the trunk selector switch for connecting a calling trunk therewith. The trunk switch is marked S and is similar in its construction to the primary selector or line switch S. The mechanical structure of this switch will be described hereinafter in connection with Fig. 7. It has a spindle s, and wipers .9 s and 8 It is rotated by means of a pawl and ratchet actuated by a vibrator magnet R and is held in the position to which it is turned by a stop pawl controlled by the release magnet The circuit of the rotary vibrator magnet is closed through an interrupter I similar to I by the sleeve relay R of the trunk and opened by the relay R, which it will be re called is controlled by the relay R, which receives current when an idle operators set has been reached. The release magnet s has its circuit controlled by contacts 0 and d actuated by the switch spindle and the relay R which is controlled by the contacts (Z and e, actuated by the switch spindle, and the relays R and R. In order to enable this description to be followed readily, I may state again that the switch S' starts up from zero as soon as the sleeve relay R of the trunk has pulled up, that is to say as soon as the trunk 17-18 comes into connection with a calling line. The wipers 8 s and s then sweep over the contacts .9 s and s of the respective operators wires, until they reach the contacts of an idle operators set, when the switch S is stopped. After the operator has performed her functions and the connection through the trunk wires 23-21 is completed to thewanted subscribers line, the release magnet 8 restores the switch S to its zero or inoperative position where it remains during the continuance of the connection.

In the lower part of Fig. 2 I have shown the apparatus which appears in front ofone operator, consisting of a set of buttons only. Above these in the figure I have buttons. These 'keys are in three sets, 7 K

and K each set having ten buttons controlling contact springs is, 10 The springs k of all the buttons in each set are joined to a common wire, and the ends of these, three common wires are connected together at the point k", from which point the conductor leads as shown in Figs. 2 and 1, to the mul tiple contacts 8 in the banks of the various trunk switches S of theanswering trunks 17, 18, 21 and 22. The spring is of each key is connected to a pen on theappropriate disk or zone'on the sending m'achinejdrum. When any particular button is depressed,

therefore, it connects its individual wire to the common wire 70. .The individual wires of the keys K are marked're'spectively 71, 72, 73, 74, 75, 76, 77, 78, 79, 80.. Similarly the individual wires from the key ,K are marked 81, 82, 83, 84,85, 86, 87, 88, 89, 90, and the individual wires of the keys Kare marked 91, 92, 93, 94, 95, 96, 97, 98,99, 100.

The sending machine comprises the main commutator D, having a brush d connected to the main battery, and riding over its seg ments so as toproduce regular recurring makes and breaks in a continuous series. In practice this commutator is made with a pair of spring contacts and teeth or cams are formed on'the body of the commutator to work these springs up and down, but for convenience of illustration I have shown the brush restingdirectly on the periphery of the disk. With such a construction in actual practice and considering that this commutator will carry a large number of switching impulses simultaneously, I prefer to make the brush d of carbon. This is a detail, however, which may be varied at will and does not aflect the invention. The commutator D is graphically shown as carried on a shaft d which extends through all of the number wheels forming both the mechanical and electrical connection therewith. The mechanical connection is not shown in the drawing but the electrical connection is indicated by a wire marked d The number wheels are shown at d, d, d, d", d d, d", ,01 d, each having a tooth or raised segment of a suitable length to cover the space of the number of teeth on the commutator D equal to the number of impulses the particular wheel is to transmit. Thus the first wheel d has a single toothd, approximately equal in length to only one tooth on the main commutator. The s cond This machine furnishes of teeth, I have all the makes and breaks on the main commutator, and in order to send any desired number of impulses, I select a wheel which will maintain connection with the commutator while the desired number of impulses are being produced and are then cut off therefrom. Another peculiarity of the arrangement is that the makes and breaks on the number wheels d, d'', d, etc., are made during the passage of gaps on the main'commutator when there is zero potential, and hence there will be no sparkmg at the number wheel contacts. In order to do this I may either subdivide the commutator surface evenly and equally into alternate conducting and insulating segments and then make each number wheel tooth slightly longer than the particular tooth to which it corresponds, or I may make the conducting portions on the commutator smaller than the insulating portions and make the number wheel teeth of lengths equal to the exact multiple of a unit subdivision.

It will be observed that there are four sets of pens on the number wheels. These will accommodate four sets of keys K, K etc. If a greater number of digits appear in the numbers to be transmitted, the wheels must be provided with additional sets of springs. The set K has its individual wires connected to the first set of springs (Z the set K has its individual wires connected to the set of springs 03, and the keys K are similarly connected to the spring pens cl. The general direction of rotation of the commutator and the various wheels connected to it is clockwise as shown by the arrows in Fig. 2, and the teeth on the wheels come in contact with the spring pens in the order (Z d, d. Thus the number set up on the set of buttons K is transmitted over the wire 70 first, then follows the number set up on the button K, and so on. Thus for the number 468 the operator would depress the fourth button in the set K, the sixth button in the set K and the eighth button in the'set K By tracing the circuits it will be found that when the controlling circuits are closed, which occurs at the beginning of a rotation when the wheels are all in the position shown in Fig. 2, current will pass from the main battery to the commutator D, thence to the wheel d thence by wire 94 to the fourth key in the set K and thence to the wire 70 and so on to the wire 19 and the relay R in Fig. 1, which repeats the impulses over trunk wire 23 to the switches. As the wheels continue their rotation, this circuit will be broken after four impulses have been transmitted, and thena .new circuit will be formed carrying current from the battery through the commutator to the sixth wheel d", and thence from the second spring d on that wheel through the w1re 86 to the ke which is closed, thence to the wire an thence again to the relay R which repeats to the switches. After these impulses have been sent by this route, this circuit will be broken and a new circuit will be formed from the main battery through the commutator D to the eighth w eel to the third pen thereon, at, thence to the eighth key in the set K which has been closed, thence to wire 70 and tothe relay R as before. The closures between the wheels and successive sets of springs area arranged to be separated by intervals, during which no current at all flows to the wire 70. These intervals are necessary in order to permit the switching circuits to be arranged so as to produce the proper results in res onse t0 the successive sets of working impu ses. In other words, having shown herein a set of Strowger switches, I must provide not only.

the vertical or working impulses in groups, but I must also provide the interposed or rotary impulses between said groups. This is accomplished by means of the wheel at" which has four teeth set in quadrature, and all adapted to make contact with the single pen d, which is connected by the wire 170 to the multiple contacts 8 in the banks of the various trunk selector switches S, and thence throughthe wire 20 to the relay R, which repeats the rotary impulses over the trunk wire 24 to the switches. The wheel d is insulated from the shaft d", and is grounded through the wire 101, this being necessary because the relay R is connected on its other side to battery wire 3. In other words, the repeating relay R which is controlled by the number wheel is a grounded relay and so the number wheels take battery impulses from the commutator to work it; but the relay R is on battery, hence the rotary wheel al uses the ground to work the relays. The reason I make one of these relays grounded and the other to battery is 1n order to pull them both up simultaneously when the operator has her telephone set bridged across the wires-7O and 170 in Fig. 3.

Hitherto the selector switch referred to as S has been referred to only as regards the electric circuits and contacts with which it 1s associated and in this connection the diagrammatic illustrations in Fig. 1 have been sufficient. The mechanical features of a switch adapted to perform the functions of the switch S of Fig. 1 are shown in Figs. 5 and 6. This switch comprises a frame a on which is mounted a bank I) of contacts consisting of .ten rows of contacts of three contacts each. The contacts of the different the stationary latch z.

rows are adapted to be successivel engaged by wipers c, (l and e which are lifted upon the rotatable shaft f, the three contacts 0, cl and 6 being respectively insulated from each other. A spring 9 interposed between the shaft 7 and a stationary part as the frame, tends to rotate the shaft 7 to one limit of movement, when the contact arms carried by the shaft will not rest upon any of the bank contacts as shown in Fig. 5. Fixed upon the shaft f is a ratchet k. The teeth of this ratchet are so constructed that a pawl engaging therewith will prevent movement of the shaft under the influence of the spring Adapted to engage with the ratchet k are a holding pawl 71 and a stepping pawl is. The pawl 71 is pivoted upon the frame'and its nose is normally held in engagement with the ratchet by means of a spring Z. The pawl 70 is pivoted to the armature m of the stepping magnet 8 which armature is in turn pivoted to the frame of the magnet or upon any other suitable stationary portion. The armature m is normally held retracted by a spring 0 while the nose of the pawl k is thrown outwardly by means of a spring p extending between the armature and the tail of the pawl k. The outward movement of the nose of the pawl la is limited and it is guided in its movement by a stationary pin g In order that the holding pawl 71 may be disengaged from the ratchet it so that the contacts upon the shaft f may be returned to their normal position under the influence of the spring g, a magnet 8', known as the release magnet is provided. The armature s of the release magnet is retracted by means of a spring t, this armature being limited in its outward movement by a nut u in screwthreaded engagement with a screw o mounted upon the frame of the magnet and extending through the armature 8 Ohviously the nut u is capable of adjustment along the screw 4: to permit greater or less movement of the armature 8 Carried by the armature s of the -release magnet is a resilient arm w which carries a ratchet tooth 00 adapted to engage with the lower end of An arm y mounted upon the armature m of the stepping magnet overlaps one end of the arm to and is adapted to draw down one end of that arm so that the lower end of the latch 2 will clear the tooth a when the armature of the stepping magnet is attracted. The operation of the apparatus is as follows Assuming the parts to be in position as shown, as impulses are supplied to the stepping magnet its armature will be attracted a number of times equal to the number of impulses and at each attraction the pawl 7.". will be thrown forward into engagement with the ratchet wheel and will move that wheel forward a distance depending upon the adjustment of the various parts, which are so adjusted that at the first impulse the wipers upon the shaft will be moved into engagement with the first row of bank contacts and will be moved to a succeeding row upon each impulse thereafter. The shaft and wipers which it carries will be prevented from ret rograde movement by the holding pawl which is forced into engagement with the ratchet h by its spring. A desired row of the bank contacts having been reached in the manner described and the object for which the connection was established having been accomplished, it becomes necessary to return the wipers to their zero or normal positions in readiness for another operation as just described. This restoration is effected by energizing the release magnet s when its armature will be attracted, drawing the tail of the holding pawl i with it, and the nose of that powl will be disengaged from the ratchet h and the wiping contacts will be returned to their initial position. In the next selective operation of the switch, however, it is necessary that the holding pawl 11 shall engage with the ratchet h to hold the contacts in an position to which they may be stepped. t, therefore, becomes necessary to releasethe pawl 11 prior to the succeeding stepping operation, a." being held by z. This is accomplished by means of the arm 3 which, upon the first energizat on of the stepping magnet and the attraction of its armature, will draw down with it the free end of the resilient arm w thereby freeing the pawl i thereupon its nose will be thrown against the ratchet h by the spring Z. (Jarried upon one of the wipers c, and e upon the shaft f, is a projection a of insulating material adapted, in the case of switches 1S etc., when the removable contacts are in their normal position, to bear against one of, and separate the contacts a and b which are so mounted as to be insulated fromeach other but which are normally in engagement.

In the particular arrangement shown, it is necessary that the switch S, instead of being released upon the energization of its release magnet, shall be released upon de energization of that magnet succeeding'an energization of it. The mechanical structure of a switch, similar to that shown in Figs. 5 and 6 but embod ing the modifications necessary to accomp ish the result indicated. is illustrated in Fig. 7.

Referring to Fi 7 the ratchet wheel h upon the wiper s aft 7" is adapted to be enga ed by a holding pawl 71' pivoted upon the rame and having its nose forced into engagement with the ratchet wheel by a spring Z. The ratchet wheel is also adapted to be engaged by a stepping pawl pivoted upon the pivoted armature of the stepping magnet R the arrangement of the step ing mechanism being the same as shown in ig.

a "retracting spring therefor and adjusting means precisely like the corres onding ortions of the switch shown in ig. 5. he tooth as on the resilient'arm w, however, when the release magnet is energized, instead of snapping behind the tail of the pawl 1." so that upon deener 'zation of the release magnet the awl wil be removed from engagement with the ratchet wheel. The arm y upon the armature of the stepping magnet overlaps the end of the arm to,

as in the case of the correspondin arms in Fig. 5, so that the holding paw is released from the arm w u on energization of the stepping magnet. hree contacts 0, at and e are so mounted upon the frame as to be insulated therefrom and from each other. The contacts 0' and d however, tend to engage at their free ends while an insulating projection 2 upon one of the wipers bears against the contact d, when the switch is in its initial position and holds that contact from engagement'with the contact 0' and in engagement with the contact 6.

The operation of the system can be best set forth by tracing the connections and noting the operations of the'various arts of the apparatus Which are involved, rom the time a call is initiated at the subscribers station until the conversation has terminated and the apparatus has been restored to its normal condition.

Let it be assumed that a subscriber at a station, as A, desires to converse. He removes the receiver from the hook when the latter rises and establishes a connection, through his transmitter and receiver, between the lines 1 and 2. A circuit is then established from the free terminal ofv the battery, B, through the wire, 3, line relay, M, armature, 12, line 1, subscribers set, line 2 and armature n to ground. The relay -M, being thus energized, attracts its armatures m and m a circuit then being established from the free side of the battery B, through conductor 3, interrupter I, armature m and conductor 8, to conductor 31 whence the circuit passes to one of the stepping magnets as s of the trunk selector switches as before explained. From the stepping magnet the circuit passes through the. conductor 8 and the armature 1- of the relay R to ground. The magnet s is then intermittently energized through the interrupter and this results in the reciprocation of the stepping pawl is (see Fig. 5) and the ste ping forward of the wipers of the switch 5 from one row of bank contacts to the next at.each energization until the wiper 14-restsupon the contact 11 to which is connected the conductor 11', leading to the front contact of the armature m, which is connected to the battery conductor 3. From the wiper 14:,v circuit is made through conductor 2'1, make-before-break contacts 28 and 29, conductor 30 and relay N' to ground. The relay N being thus energized attracts its armatures 1 21- and 211 and connects the trunk conductors 1'7 and 18 with the trunk ext-ensions 15 and 16 which are connected to the wipers 12 and 13 respectively.

'hen the wiper 14 rests on the contact 11, the wipers 12 and 13, rest-on the contacts 9 and 10 respectively. The cut-ofi' relay N is therefore connected in series with the relay R in a circuit which can be traced from the ground through relay N, extension 5, contact 10, wiper 13, extension 16, armature 111, trunk wire 18 and relay R to the free side of the battery. The relay N is of high resistance compared to that of relay R and R and operates on less current so that while the relay N is operated, the relay R is not operated by reason of the circuit just traced. The relay N, however, is of such resistance that it will carry sufiicient current, after the relay R is connected, to hold its armatures after they have been attracted. -The relayN being thus energized, attracts its armatures, thereb breaking the circuit of the line relay at the armature o2. whereupon the relay M is deenergized and its armatures fall back, thereby breaking the circuit of the stepping magnet 8 whereupon the switch stops. The attraction of its armatures by the relay N,

connects the subscribers lines 1 and 2 with the extensions 4 and 5, contacts 9 and 10, wipers 12 and 13, trunk extensions 15 and 16, armatures 2n and 1a and trunk conductors 17 and 18 respectively. It will now be seen that the tip and sleeve relays R and R are connected by means of the connections just traced, in series through the subscribers instrument and between battery and ground.

The relays R and R being energized, their armatures will be attracted, whereupon the circuit of the release magnet s will be broken at the armature r and the armature 11* will come against its front contact 29 which it separates from contact 28, the battery connection of the former contact being maintained through the conductor 40. The armatures 21' and 37' are removed from their back contacts thereby breaking the battery connections which otherwise would be established with the trunk conductors 21 and 22 upon the attraction of the armature 27- of the relay R. The armature 1" of the relay R on being attracted, leaves its back contact and thus breaks the circuit through the stepping magnet s and, coming against its forward contact, makes grouncl' connection, through conductor 41 for the stepping magnet 18 of the next trunk selector switch, as before explained. The attraction of the armatures 1r and 2r establishing of ground connections through one terminal of that relay.

Circuit may now be traced from the ground through the armature 1r, conductor 12. armature 1' conductor 44, stepping magnet R interrupter I and conductor 45, to the battery wire. The magnet B being intermittently energized will reciprocate its pawl, (see Fig. 7 and description thereof) stepping the switchforward.

A function of the relay R is to prevent interference with the connecting operation by reason of the passage of the wipers of the switch S over the contacts 8 s and s of busy operators sets. The relay R having been energized by the connection of the subscribers line to the trunk, circuit may be traced from the ground through the armature 21", conductor 43, armature 1r, conductor 102, relay R conductor 101, contacts d and e which are normally open,

but are closed when the wipers of the switch S are in ,their initial position, to battery. In this initial position, therefore, the relay R is energized through the circuit traced position, the contacts at and 6 separate but the .battery connection is maintained so long as the wiper s is passing over busy con tacts s as, where those contacts are busy, the armature 21" will be attracted and circuit to the battery from each of these contacts will be made by the armature just referred to. When, however, an idle contact is reached, the circuit of the relay R is broken and is subsequently maintained opened by the energization of the relay B, when the circuit of the relay R is broken at the armature 17". A further function of the relay R is to aid in controlling the release magnet s as hereafter will appear.

The stepping relay R having its circuit closed, as described, the switch S will be stepped from one position to the next so that its wipers s, 8 and s will pass successively over the rows of bank contacts 8 s and 8 Upon the arrival of wiper 8 upon the contact a, circuit may be traced from the free side of the battery B through armature r conductor 110, magnet R contact 111, contact 112, conductor 113,

contact 8 wiper 8 conductor 19, armature 1' conductor 114 and relay R to ground. The relays R and R are thus connected in series and this results in the attraction of their armatures. The' attraction of the armature r of the relay R however, results in the connection of that contact of the armature r with the contact 115 of conductor 106, when circuit may be traced from the conductor 3 through the armature 1", contact 115, conductor 106, relay R conductor 43 and armature 21" to ground. The relay R is. thus momentarily energized and attracting its armature 2r brings that armature against the contact 116, thereby transferring the battery connection of the relay R from that made through armature r to that made through armature 2r and conductor 107 to the conductor 3 and the free side of the battery. The relay R thus locks its own circuit so that it remains energized after the relay R has become de'e'nergized. The relay R, being thus energized, its armature will be attracted, thus breaking the circuit of the stepping magnet R whereupon the switch S will stop. The relay R attracts its armature 11", thereby breaking the circuit at this point of the relay R whereupon its armatures fall back and connect the operators wires 19 and 20 with the trunk circuits. The releasing of the armatures of the relay R also results in. the falling of the armature 21 against its back contact which is connected to ground while the armature is connected to the release magnet s and therefore one terminal of that magnet is grounded.

After the switch S has left its initial position, the contacts 0" and d come into engagement, thus connecting one terminal of the release magnet s with the conductor 101. When, therefore, an idle operators equipment has been selected, a battery connection for the release magnet is made through the wiper 8, contact 8 conductor 121 and armature 21" to battery wire 3. The relay R being then deenergized, the magnet s is energized and the release mechanism becomes set, as before described, to release the switch S upon the deenergization of its release magnet.

The relay R having been energized as described, its armatures 17' and 21' will be attracted and circuit can be traced from the battery wire through the armature 1r, conductor 120 and the lamp L to ground. The lamp will thus become lighted, notifying the operator of a call. Another circuit can be traced from the battery wire through the armature 27- and conductor 121 to the contact 8, whence circuit will be traced through the wiper s conductor 101, relay R and conductor 102 to a back contact of the armature 1r, but at this point the circuit is oggned, due to the energization of the relay Connection may now be traced from the conductor 17 0 through-the'contact s, wiper 8 conductor 20, armature 1r of the relay R conductor 124, conductor, 125 and relay R to battery wire 3. Connection 'may also be traced from the wire through contact a, wiper 8 conductor 19, armature r of relay R,conductor 114 and relay R to ground.

Referring now to Fig. 2, it will be seen that the conductors 170 and 70 are adapted to be connected by means of the pressure of a' button 0 with conductors 127 and 128, which lead tolamoperators set of usual construction and-hence not shown. It will be seen that upon the de ression of the button 0, that a circuit will e completed from the battery wire at one side of the relay R through that relay the operators set, and the relay R to ground. Talking current will thus be supplied to the operators set and also the relays R and R will become energized, whereupon they will attract their respect1ve armatures 1r and r and one of the operators conductors 20 will be connected with the trunk conductor 21 while the other operators conductor 19 will be connected with the other trunk conductor 22. It will now be apparent that the operators set and the calling subscribers instrument will be so connected that conversation may be had.

The operators set and subscribers instrument having been-placed in conversational communication as described, the operator inquires of the subscriber the number of the wanted subscribers station. Let it be assumed that this number is 468. The operator depresses the fourth key of the set K, the sixth key of the set K and the eighth key of the set Kl. In this manner the conductors 94, 86 and 78 are connected with the common point law, these conductors being respectively connected with the pen 03 of the section drum d, the pen (i of the drum section 03 and the pen d of the drum section (i The commutator D is driven by a motor M and, the motor supposed in the particular apparatus shown to be normally at rest, it becomes necessary to start the motor and commutator. To accomplish this, the operator depresses the button 0 and thereby connects the conductor 130, which is connected to one terminal of battery to the conductor 131 and thence through the conductor 132 to the relay R and to ground. The relay R being thus energized, its armatures 1' and 11' are attracted when circuit will be closed from the battery wire through the 'last mentioned armature, conductor 133 and relay R to ground. The relay R being thus energized, will atti act its armatures r and 11 The circuit of the relay R to battery through the armature r is thus broken, but this connection is made through the armature 1' of the relay R whereby the control of the relay R is transferred from the relay R to the relay R Circuit may be traced also from the motor conductor 134 through the armature 11' and a suitable generator and motor starter as indicated, which may beof any well known or suitable type, to the other motor conductor 135. The motor will thereupon start up and place the commutator in operation. There is also set in operation a starting disk ds, which is of conducting material with the exception of an insulating segment 136 upon which the pen 137 normally rests. After the motor and with it the commutator, starting disk, rotary disk and drum sections are set in operation by the depression of the key 0, as

described, the pen 137 will ride oil the insulating segment and maintain the circuit initially closed by the depression of the but-' ton This circuit being closed, the motor, commutator and disks will continue to revolve until the pen 137 rests upon the insulating segment 136, when the circuit will be broken and the apparatus will stop. During this rotation, first the pen at, corresponding to the disk 03*, will be engaged by the contact segment upon the said disk, which is of such a length as to maintain the contact with the pen during four impulses of current through the commutator. The circuit over which these impulses are sent, may be traced from one terminal of the battery to the brush-d, thence through the commutator,the conductor do to the shaft of the drum, thence through the drum to the segment of the disk d, the pen of", the conductor 94, the contacts of the fourth button of the row K to the point 7cm, thence through the conductor to the contact 8 of the switch S, conductor 19 and relay R to ground. At each of the four impulses, the relay R will be energized and attract its armature 275 against its back contact, connected with the battery 13. At each impulse, therefore, the tip side 23 of the trunk will be connected with battery and the impulses will be repeated over this side of the trunk to operate the automatic selector and connector switches as before described; the next the battery wire 3. Each projection on the disk d" is of such length as to transmit but one impulse and this impulse passing through the rela R through the circuit just traced, the re ay last mentioned attracts its armature 11' against its back contact, thereby connecting the sleeve side 24 of the trunk momentarily with the battery wire 3, when a rotary impulse is transmittedover the sleeve side for working the side switches of the automatic selector and connector switches as before indicated; after the sending of the rotary impulse described, the conducting segment of the disk d comes in contact with its'pen 03, when six impulses are sent over the conductor'86 to the point km, whence circuit is the same as before, through the rela R and six vertical impulses are transmitted over the tip side 23 of the trunk. The disk (1 then sends another rotary impulse over the sleeve side of the trunk as before and eight vertical impulses are then transmitted over the tip side by reason of the contact upon the disk d coming in contact with its pen d, connected with the conductor 78 through which connection is established to the point km, the circuit being otherwise the same as before, through the relay R and eight vertical impulses will be transmitted over the tip side 23 of the trunk; this is followed by the sending of a rotary impulse by the disk at and then the apparatus is brought to a stop by reason of the pen 137 riding upon the insulating segment 136. p

At the close of'the operation just described, the wanted subscribers line, unless it is busy, will have been connected as below described. The entry of the pen 137 uponthe insulating segment. 136 at the end of the connecting operation, breaks the circuit as before traced through the relay R", which thereupon releases its armature, thereby breaking the circuit of the relay R which in turn releases its armatures, thereby breaking the circuit of the release magnet 8 when (see Fig, 7) the holding pawl 71 will have its nose removed from engagement with the ratchet upon the switch shaft and the switch will return to its zero position, thus leaving the operators set idle in readiness to perform the connecting operation for another connecting trunk and its subscribers instrument.

The circuit of the relay R will be broken cuit of the vertical magnet v, and thereby steps the spindle of switch S' up to the fourth row of contacts. A'single rotary impulse then comes over the trunk wire 24, energizing the rotary relay which is normally connected through the switch arm .5 as shown, and which in turn closes circuit of the private relay T, which pulls up, opens the circuit of the vertical magnet 0, and mechanically releases by one step the escapement which holds the spring actuated side switch arms s 8", 8 8. All these arms pass into the second position, the arm s grounding the rotary magnet 22 which is connected on the other side to the main battery B, and is adapted to make and break its own circuit so as to form a vibrator. This magnet then steps the switch spindle around so that the wipers 8 8 will sweep over the row contacts 8 and s of the ten trunks in the 400 group, testing them for an idle trunk, by successively closing circuit from the contacts 8 through the wiper 8 and the low resistance release relay Q to the test or private relay T. As long as only ground contacts are found, due to their trunks being busy, so long .will the relay T be held up as it is in the test circuit with the relay Q. As soon as an ungrounded contact is found, the relay T lets go, and kicks the escapement over the second step, so that all side switch arms step off the middle contacts and get on the last ones, the arm 8 thus cutting off the rotary magnet and stopping the rotation, the arms 8 and s completing the talking circuit and disconnecting the vertical and rotary relays therefrom, and finallqy the arm a disconnecting the test relay and grounding the wiper 8 through the relay Q, for release purposes.

This operation has connected the trunk wires 23 and 24 to an idle trunk in the 400 group, which we will assume to be the trunk 4344. To select line 53 in this group five impulses come over wire 23 to the vertical relay V which grounds the vertical magnet o five times, and steps the spindle of the switch S up to the fifth row of contacts. A single impulse then comes over the rotary side 24 and works the rotary relay V which closes the circuit of the relay T, which in turn kicks over the escapement controlling the side switch arms 8 8 8 8 so they will get onto their second contacts. This cuts off the vertical magnet 0 and cuts on the rotary magnet '0 Three more impulses now come over the vertical trunk wire 23 again working the relay V, which however now closes three times in succession the circuit of the rotary magnet 12 which steps around the spindle of the switch S so that the wipers S will rest on the third pair of contacts in the fifth row in the banks of that switch. These are the contacts of line No. 453.

A single rotary impulse now comes over the wire 24 which pulls up the relay V and closes the test circuit of .relay Q as nector switch, which will thereupon restore.

When the calling subscriber hangs up his receiver, and the relay R lets go, simultaneous impulses over the Wires 21-23 and 2224 will energize both relays V and V which will close the release circuit 39, s, 38, Q, 8 8, 64, 52, 51 and battery B. The release relay Q, of the switchS will then pull up and close the circuit of its release magnet 9 whereby the selector switch Stwill be restored. The circuits of the relays V V are as follows: for V from B (Fig. 1), 107, 27", 116, 106, 21", 21, 2r, 23, (Fig. 3) 8 '8", 8 V and ground to battery; for V from B (Fig. 1), 107, 21", 116, 106, 31', 22, 11'", 24 (Fig. 3), s 8 8 V and ground back to battery.

If the line tested is not busy nothing will happen until after the cessation of the test impulse, but the switch arms 8 8, 8 s will then be kicked over to their third po sition, completing the talking circuit to the wipers .9 when the relay R will immediately pull up because of the completion of its circuit through the line cut-off relay of the selected line as follows: B, 3, 50, R 8, 8 (see line connections in Fig. 1 which are identical), 10, 5, N, ground and back to battery. As soon the sleeve relay R pulls up, the ringing relay R will pull up, completing the following circuit: B, 3, 50, 49, 48, 47, R, 45, interrupter K and ground. The ringing relay R will then connect the ringing generator Gr so as to send its current out over the wanted line at intervals determined by the commutator K. When the subscriber answers, direct current will flow to his line in the intervals of actuation of the relay R and at such time the tip relay R will pull up, closing the circuit of the ringing cut-ofl relay R which disconnects the ringing relay and locks itself on a circuit extending direct from the battery through its own armature on one side and through a pair of spring contacts opened by the spindle of the switch S when it is down and closed whenever it is off normal. The relay R is introduced to revent ringing back a party after he has ung up.

The release of the switches and the general clearing out scheme has already been sufficiently described in connection with the test.

While I have stated that these switching circuits in Fig. 3 are old and well known,

the relay R, whereupon its armatures arereleased. Its armatures will thereupon be released'and fall back and circuit will be traceable from the round through magnet 8', armature 7, con uctor 106, armature 21" and conductor 107 to battery. The release magnet will be ener ized and (see Figs. 5 and 6) the switch 5 will be released and returned to its initial position. When the wiper 13 leaves the contact 10, the circuit through the relays N and R will be broken, whereupon their armatures will be released. The releasing of the armature 21" breaks the circuit of the relay R and its armatures are released. The battery connection to the wire 106 is then broken at the armature 21 It is to be noted, however, that the relay R is'not deenergized until after the relay R has been deenergized and its armatures, including 21' and 31' have been released. This being the case, it will be seen that the two sides 21 and 22 of the trunk are simultaneously connected with battery.

-This results in the simultaneous energization of the relays V and V the circuit of the relay V being traceable from the trunk conductor 43 through the relay V and conductor to ground, while the circuit of the relay V is traceable from the trunk conductor 44 through relay V to ground. Relays V and V having been thus energized and thein armatures attracted, circuit may be traced from battery wire 51, release relay Q, conductor 52, conductor 64, bank contact 8 wiper 8 release relay Q, conductor 38, side switch arm 8 and conductor 39 to ground. The release relays Q and Q being thus energized, will attract their armatures when the circuits of the release magnet g and g of the switches S and S respectively will be closed, whereupon those switches will be released and will return to their normal positions. The apparatus will then be in its normal inactive condition in readiness for another call.

Having thus described my invention what I claim and desire to secure by Letters Patent is:

1. In a telephone exchange system, a

number of subscribers lines, a number of trunks less than the number of lines, each trunk terminating at one end in a primary selectorswitch and at the other endin a first'selector switch, a plurality of operators circuits and apparatus, each of said operators circuits including a telephone set and sending device, and an automatic switch associated with each of said trunks and containing terminals of a number of said operators circuits, each of the switches specified being normally in a zero or inoperative position, and adapted to be started up to test and connect with bank terminals in their numerical order, substantially as described.

2. In a telephone exchange system, a number of subscribers lines, a number of trunks less than the number of lines, each trunk terminating at one end in a primary selector switch and at the other end in a first selector switch, a plurality of operators circuits and apparatus, each including a telephoneset and a sending device, and an automatic switch associated with each of said trunks and containing terminals of a number of said operators circuits, to ether with release or restoring means or all of said switches, substantlally as described.

In a telephone exchange system, a number of subscribers lines, a number of trunks less than the number of lines, each trunk terminating at one end in a primary selector switch and at the other end in a first selector switch, a plurality of operators circuits and apparatus, each including a telephone set and a sending device, and an automatic switch associated with each of said trunks and containing terminals of a number of said operators circuits, together with driving means for the primary selector switches controlled by the calling subscribers, and driving means for the operators switches controlled by the primary selector trunks, substantially as described.

4. In a telephone exchange system, a number of subscribers lines, a number of trunks less than the number of lines, each trunk terminating at one end in a primary selector switch and at the other end in a first selector switch, a plurality of operators circuits and apparatus, each including a telephone set and a sending device, and an automatic switch associated with each of said trunks and containing terminals of a plurality of said operators circuits, together with driving means and release or restoring means for the primary selector switches controlled by the calling subscribers, and driving means for the operators selector switches controlled in the use of the primary selector trunk, substantially as described.

5. In a telephone exchange system, a number of subscribers lines, a number of trunks less than the number of lines, each trunk terminating at one end in a primary 

